Examples of a high pressure fuel injection system are shown in U.S. Pat. No. 4,081,140 issued to Kranc on Mar. 28, 1978, U.S. Pat. No. 5,020,500 issued to Kelly on Jun. 4, 1991, and U.S. Pat. No. 5,191,867 issued to Glassey et al. on Mar. 9, 1993. Engines equipped with high pressure fuel injection systems have an optimal volumetric injection rate. For diesel-cycle engines, this optimal injection rate has a gradual rise, a period of stabilization, followed by a sharp drop. Means of producing this characteristic profile are commonly referred to as rate shaping means or devices because they are used to shape the volumetric rate of fuel injection into an engine combustion chamber. The gradual rise followed by a sharp drop in fuel injection has the specific benefit of minimizing particulate emissions from combustion. It also minimizes combustion noise.
Fuel injector nozzles typically include a housing or tip with an elongated cavity or void along a first axis. At least one injection orifice fluidly connects one end portion of the cavity with an atmosphere (e.g., engine combustion chamber) external to the fuel injector. A needle check is slidably disposed within the cavity for translation between a first position in which a first end portion of the needle check seats against a seat of the tip, wherein the first end portion of the check is seated against the seat, covering or blocking the injection orifice(s), and a second position wherein the first end portion of the check is spaced from the seat and does not block the injection orifice.
In the fuel injector of Glassey et al., a spring is disposed between the needle check and the housing, tending to bias the needle toward the first position. Pressurized fuel directed to a portion of the cavity in which the first end portion of the check is disposed overcomes the spring to move the check away from the seat to the second position. Fuel is transferred from a fuel pumping chamber in which the fuel is pressurized, directly to that portion of the cavity, a fuel injection chamber, in which the first end portion of the check is disposed without the benefit of rate shaping.
The fuel injector nozzle disclosed by Kranc has a valve disposed between a fuel pumping chamber, and a first end portion of the cavity in which the needle check is disposed. However, the valve of Kranc provides essentially an on-off control of flow to the injection chamber. This does not provide the gradual rise in flow rate desired for fuel entry into the injection chamber at the beginning of the injection cycle.
Kelly discloses a fuel injector in which flow is varied as a function of lift height of the check from the seat, with flow restricted from the first position to a predetermined midpoint to provide the desired gradual rise in flow. The flow is relatively unrestricted from the midpoint to the second position. However, Kelly does not teach the use of a second valve or check to control fluid flow to the needle check.
It is desired to provide a fuel injector nozzle having a valve disposed between the pumping chamber and the fuel injection chamber which restricts the transfer of fuel to the first end portion of the check within injection chamber to a relatively low initial rate followed by a higher rate of flow with displacement of this valve.